I want to use my Blackjack II, but I can't find a Japan carrier/plan that'll let me use the unlocked phone.?

Hey I have a question regarding the Blackjack II in Japan. I have a phone plan in the States, but since I'll be working in Japan for 2 years, I will also have a phone plan in Japan. I unlocked the Blackjack II, so that I would be able to use the network in Japan. However, I've been having trouble finding a service that will let me use their sim card in my Blackjack II. Can you help me out? I want to use my Blackjack II, but I can't find a carrier that'll let me use the phone.